Bright colorful flowers rising above neat mounds of delicate foliage make corydalis perfect for shady borders. The foliage may remind you of a maidenhair fern, and both the flowers and foliage look great in cut flower arrangements. The plants have a long flowering season that may last from spring until frost.
What is Corydalis?
Corydalis plants are close relatives of bleeding hearts, and you can see the resemblance in shape between corydalis flowers and small types of bleeding hearts. The genus name “Corydalis” derives from the Greek word ‘korydalis,’ which means crested lark, referring to the similarity between the flowers and spurs to a lark’s head.
Of the 300 or so species of corydalis – with differing colors available, the two types that you see most often in North American gardens are the blue corydalis (C. flexuosa) and yellow corydalis (C. lutea). Blue corydalis reaches a height of 15 inches with a similar spread, while yellow corydalis grows a foot tall and wide.
Both blue and yellow corydalis needs full sun or partial shade and moist but well-drained, organically-rich soil in USDA plant hardiness zones 5 through 7. It prefers a neutral or alkaline pH soil as well.
Water often enough to keep the soil moist and feed the plants with a shovelful of compost or a gentle organic fertilizer in spring before the buds begin to open.
These plants don’t generally need pruning other than removing spent flowers to prevent unwanted self-sowing and prolongs the bloom season.
Corydalis plants may die back where winters are cold or summers are hot. This is normal and not a cause for concern. The plant regrows when temperatures improve. Planting them in a moist, shady area where summer temperatures are hot may help prevent summer dieback.
You’ll have no trouble propagating corydalis by division in fall after the last of the flowers fade. Corydalis is a bit fussy to start from dried seeds, but freshly collected seeds germinate readily. They grow best if kept in the refrigerator for six to eight weeks in a dry, air-tight container. After chilling, sow them at 60 to 65 F. (16-18 C.) on the surface of the soil. They need light to germinate, so don’t cover them. You’ll have better luck sowing the seeds directly in the garden.
Corydalis self-sows readily. You can transplant the seedlings to a better location when they have several true leaves. They may become weedy if left to reseed themselves, but coarse mulch around the plants can prevent them from becoming aggressive.